From: Dave Thaler <dthaler@xxxxxxxxxxxxx> Explain helper functions Signed-off-by: Dave Thaler <dthaler@xxxxxxxxxxxxx> --- Documentation/bpf/instruction-set.rst | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst index aa1b37cb5..40c3293d6 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -242,7 +242,7 @@ BPF_JSET 0x40 PC += off if dst & src BPF_JNE 0x50 PC += off if dst != src BPF_JSGT 0x60 PC += off if dst > src signed BPF_JSGE 0x70 PC += off if dst >= src signed -BPF_CALL 0x80 function call +BPF_CALL 0x80 function call see `Helper functions`_ BPF_EXIT 0x90 function / program return BPF_JMP only BPF_JLT 0xa0 PC += off if dst < src unsigned BPF_JLE 0xb0 PC += off if dst <= src unsigned @@ -253,6 +253,22 @@ BPF_JSLE 0xd0 PC += off if dst <= src signed The eBPF program needs to store the return value into register R0 before doing a BPF_EXIT. +Helper functions +~~~~~~~~~~~~~~~~ +Helper functions are a concept whereby BPF programs can call into a +set of function calls exposed by the eBPF runtime. Each helper +function is identified by an integer used in a ``BPF_CALL`` instruction. +The available helper functions may differ for each eBPF program type. + +Conceptually, each helper function is implemented with a commonly shared function +signature defined as: + + u64 function(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) + +In actuality, each helper function is defined as taking between 0 and 5 arguments, +with the remaining registers being ignored. The definition of a helper function +is responsible for specifying the type (e.g., integer, pointer, etc.) of the value returned, +the number of arguments, and the type of each argument. Load and store instructions =========================== -- 2.33.4
